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Study focuses on ocular higher-order aberrations in eyes with congenital ptosis
There were some significant differences in higher-order aberrations between ptosis eyes and normal fellow eyes.
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Congenital upper lid ptosis is characterized by the drooping of the upper lid since childhood due to the maldevelopment of the levator muscle, as seen in Figures 1 to 3. It is considered as the simple type when there is no abnormal eye movement, jaw winking phenomenon, strabismus or innervational abnormality.
It has been known that the long-standing upper lid abnormality can induce corneal surface alterations. We now report on an analysis of ocular higher-order aberrations in congenital ptosis; until now, there have been no reports on the subject. In this article, we have analyzed the ocular higher-order aberration profile of patients with unilateral congenital ptosis and compared results with their normal fellow eyes.
Study
Our study was an observational comparative case series of higher-order aberration profiles of patients with unilateral congenital ptosis. Patients were recruited from an oculoplastic specialty clinic of Dr. Agarwal’s Eye Hospital and Eye Research Centre. Patients who were uncooperative, younger than 5 years old, or had complicated congenital ptosis, tear film abnormality, abnormal Bell’s phenomenon, high ametropia of more than 2 D or a history of ocular surgery were excluded.
Ocular higher-order aberrations were measured using the Zywave workstation (Bausch + Lomb), a device based on the Shack-Hartmann principle. All aberrometry measurements were taken between 2 p.m. and 6 p.m. to compensate for diurnal variation. Aberrometry readings were taken in both the ptosis eye and fellow eye by a single examiner. There were 23 congenital ptosis eyes of 23 patients, out of which there were nine right eyes and 14 left eyes with congenital ptosis.
Figure 1. Ptosis with head tilt.
Images: Agarwal A
Figure 2. Mild ptosis.
Figure 3. Severe ptosis.
There was a significant difference (P = .005) noted in the third-order Zernike coefficient vertical trefoil (z331) between the ptosis and fellow eyes. The mean z331 was –0.13 ± 0.17 in the ptosis eyes and –0.03 ± 0.13 in the normal eyes. There was no significant difference in vertical coma, horizontal coma or total coma. There was a significant difference in the fourth-order z421 (P = .041) and z420 (P = .027) coefficients. There was a significant difference (P = .008) in total root mean square between the ptosis and normal eyes.
Discussion
It is proven that the change in lid position during daily activities can affect corneal topography and ocular aberrations. Eyelid position during tasks is an important factor that makes the difference in the aberrations. In our series, there was a definite decrease in palpebral aperture height noted in the ptosis eyes. It was noted that vertical trefoil differed significantly in the third-order aberrations and secondary astigmatism in the fourth-order aberrations. However, there was no significant difference in coma or spherical aberration between the ptosis eyes and normal fellow eyes. It was interesting to see the trefoil altered in the ptosis eyes instead of coma, as one may expect. However, total coma and coma-like aberrations correlated with marginal reflex distance and corrected distance visual acuity of ptosis eyes. We know that vertical orientation of trefoil is significantly more frequent in normal eyes, and it has been shown that the interaction of vertical trefoil with coma improved visual acuity more than when they acted independently.
We observed that, compared with normal fellow eyes, congenital ptosis can induce changes in higher-order aberrations. However, there are many higher-order aberrations that did not differ from the normal eyes. It is known that uncompensated higher-order aberrations can cause subnormal vision. We have previously termed this as “aberropia.” However, in congenital ptosis, stimulus deprivation has to be ruled out because there was no significant difference in vertical trefoil between the normal and ptosis eyes, depending on the severity of ptosis. This gives the clue that stimulus deprivation is a major factor for the difference in vision in these eyes.
Although there is a narrowed palpebral aperture in congenital upper lid ptosis, unlike myopes, these patients do not squeeze eyes. There is uniform pressure distribution in congenital ptosis, unlike mechanical drooping of the upper lid, which induces localized pressure on the eye. Moreover, most of these patients develop a head position to see that, again, will prevent pressure on the eyes. These may be the reasons why the ptosis eyes showed no significant changes from the normal fellow eyes in most of the ocular higher-order aberrations.
The small sample size is one main limitation of the study, and further evaluation in a larger group and serial follow-up comparison after surgical correction are needed. The aberrations in eyes with severe ptosis were recorded after mechanical elevation of the lid, and this can change the aberrations in the short term. Another limitation is the wide age range of the study population (range: 7 years to 35 years). Nevertheless, we believe that this study will let us think in a new way about variations in ocular higher-order aberrations in eyes with congenital ptosis, a common eyelid problem in oculoplastics. An analysis of ocular higher-order aberrations in children younger than 15 years old with congenital ptosis is currently under evaluation. However, a large population study with varied etiology of ptosis is required in the future.